## Definition

Compressibility factor of gases is a thermodynamic property which is used to modify the ideal gas equation for real gases.

For Ideal gases, Ideal gas equation states,

PV = nRT

This equation can be modified for real gases, to be expressed as,

PV = ZnRT, here Z is the compressibility factor for the given gas.

The compressibility of a gas depends on the particular gas as well as temperature and pressure conditions. You can use different equations of state for calculating the compressibility factor of a gas as a function of temperature and pressure.

These equations of state have provided formula to calculate Z factor. The constant parameters used in these equations are empirically determined for a gas. For example, compressibility factor for natural gases.

## Compressibility is a function of reduced Temperature and Pressure

You can use compressibility charts available from literature to calculate the Z factor for different gases at given temperature and pressure conditions. You can calculate the Z factor as a function of the reduced temperature and reduced pressured, using these charts.

Reduced temperature, T_{r} = T / T_{c}

Reduced pressure, P_{r} = P / P_{c}

where T_{c} and P_{c} are critical temperature and pressure values respectively.

Some correlations such as Pitzer correlations, use the gas reduced properties such as reduced temperature and reduced pressure to approximately calculate the Z factor. You can also use EnggCyclopedia's Z factor calculator to calculate the compressibility factor based on such correlations.